This invention relates generally to balancing vehicle wheels and more particularly, to methods and systems for matching vehicle wheels using a balancer that includes a load roller.
At least some known vehicle wheel assemblies use tires comprising a number of different material compositions. Some of such compositions may be more susceptible to a condition commonly referred to as “flatspotting.” Recent evidence suggests that the flat spotting problem has been escalating because of the increased use of low profile, increased sidewall stiffness tires. Most often the flat spotting is caused by the vehicle sitting in a parking lot, especially in hot weather. Extreme cases occur with long term vehicle storage by dealerships. When a vehicle stands for an extended period of time, those portions of the tires which are in contact with the ground flatten to match the ground surface. The flattened portion tends to be retained for a substantial period of time after the vehicle is placed in operation. As the tire rotates, there is a noticeable thumping or slapping sound resulting from the flat spot on the tire. With many tire compositions, the flat spot runs out quickly. However, the properties of some tire compositions are such that the flatspotting is retained substantially longer than with other tires or may become permanent.
Although severe radial force variation issues can be caused by flat spotted tires, no known wheel balancers are able to recognize a flat spot. Known techniques require the flat spot to be massaged out of the tire before balancing and/or computing the matching mark locations for the rim and tire, therefore errors and an improper diagnosis occur for this possibly temporary condition. For example, an original equipment manufacturer technical service bulletins requiring repair shops to drive vehicles for twenty miles in hopes of massaging out flat spots. Not only is this an unreasonable task for shops to perform but they have no way of knowing if any of the tires are even flat spotted to begin with. Time constraints prevent shops from driving every car for twenty miles “just in case.” Additionally a flat spot introduces higher order harmonics into a radial force variation measurement that are not typically utilized for diagnosing tire conditions.